TIMING SYNCHRONIZATION FOR DOWNLINK (DL) TRANSMISSIONS IN COORDINATED MULTIPOINT (CoMP) SYSTEMS

ABSTRACT

Technology for adjusting a receiver timing of a wireless device in a Coordinated MultiPoint (CoMP) system is disclosed. One method can include the wireless device receiving a plurality of node specific reference signals (RSs) from a plurality of cooperating nodes in a coordination set of the CoMP system. The coordination set includes at least two cooperating nodes. The wireless device can estimate a composite received RS timing from a plurality of received RS timings generated from the plurality of node specific RSs. The received RS timings represent timings from the at least two cooperating nodes. The wireless device can adjust the receiver timing based on the composite received RS timing. A node specific RS can include a channel-state information reference signal (CSI-RS).

RELATED APPLICATIONS

This application claims the benefit of and hereby incorporates byreference U.S. Provisional Patent Application Ser. No. 61/556,109 filedNov. 4, 2011, with an attorney docket number P41399Z.

BACKGROUND

Wireless mobile communication technology uses various standards andprotocols to transmit data between a node (e.g., transmission station)and a wireless device. Some wireless devices communicate usingorthogonal frequency-division multiplexing (OFDM) combined with adesired digital modulation scheme via a physical layer. Standards andprotocols that use OFDM include the third generation partnership project(3GPP) long term evolution (LTE), the Institute of Electrical andElectronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m),which is commonly known to industry groups as WiMAX (Worldwideinteroperability for Microwave Access), and the IEEE 802.11 standard,which is commonly known to industry groups as WiFi.

In 3GPP radio access network (RAN) LTE systems, the node can be acombination of Evolved Universal Terrestrial Radio Access Network(E-UTRAN) Node Bs (also commonly denoted as evolved Node Bs, enhancedNode Bs, eNodeBs, or eNBs) and Radio Network Controllers (RNCs), whichcommunicate with a wireless device (e.g., mobile device), known as auser equipment (UE). A downlink (DL) transmission can be a communicationfrom the node station (or eNodeB) to the wireless device (or UE), and anuplink (UL) transmission can be a communication from the wireless deviceto the node.

In homogeneous networks, the node, also called a macro node, can providebasic wireless coverage to wireless devices in a cell. The cell can bethe area in which the wireless devices are operable to communicate withthe macro node. Heterogeneous networks (HetNets) are used to handle theincreased traffic loads on the macro nodes due to increased usage andfunctionality of wireless devices. HetNets can include a layer ofplanned high power macro nodes (or macro-eNBs) overlaid with layers oflower power nodes (micro-eNBs, pica-eNBs, femto-eNBs, or home eNBs[HeNBs]) that can be deployed in a less well planned or even entirelyuncoordinated manner within the coverage area (cell) of a macro node.The lower power nodes (LPNs) can generally be referred to as “low powernodes”. The macro node can be used for basic coverage, and the low powernodes can be used to fill coverage holes, to improve capacity inhot-zones or at the boundaries between the macro nodes' coverage areas,and improve indoor coverage where building structures impede signaltransmission. Inter-cell interference coordination (ICIC) or enhancedICIC (eICIC) may be used for resource coordination to reduceinterference between the nodes, such as macro nodes and low power nodesin a HetNet.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the disclosure will be apparent from thedetailed description which follows, taken in conjunction with theaccompanying drawings, which together illustrate, by way of example,features of the disclosure; and, wherein:

FIG. 1 illustrates a diagram of an orthogonal frequency-divisionmultiplexing (OFDM) symbol transmission from a macro node and a lowpower node (LPN) in coordination set and a received OFDM symbol at awireless device and adjusting a fast Fourier transform (FFT) windowusing an earnest received reference signal (RS) timing in accordancewith an example;

FIG. 2 illustrates a diagram of an orthogonal frequency-divisionmultiplexing (OFDM) symbol transmission from a macro node and a lowpower node (LPN) in coordination set and a received OFDM symbol at awireless device and adjusting a fast Fourier transform (FFT) windowusing reference signal received power (RSRP) and received referencesignal (RS) timing in accordance with an example;

FIG. 3 illustrates a diagram of an orthogonal frequency-divisionmultiplexing (OFDM) symbol transmission from a plurality of cooperatingnodes in coordination set and a received OFDM symbol at a wirelessdevice and adjusting a fast Fourier transform (FFT) window usingreference signal received power (RSRP) and received reference signal(RS) timing in accordance with an example;

FIG. 4 illustrates a diagram of an orthogonal frequency-divisionmultiplexing (OFDM) symbol transmission from a plurality of cooperatingnodes in coordination set and a received OFDM symbol at a wirelessdevice and adjusting an inverse fast Fourier transform (IFFT) window ofa first cooperating node using an adjustment timing in accordance withan example;

FIG. 5 illustrates a block diagram of radio frame resources inaccordance with an example;

FIG. 6 depicts a flow chart of timing synchronization for a downlink(DL) transmission In a Coordinated MultiPoint (CoMP) system inaccordance with an example;

FIG. 7 illustrates a block diagram of the physical layer of atransmitter and receiver in an orthogonal frequency-divisionmultiplexing (OFDM) wireless network in accordance with an example;

FIG. 8 depicts a flow chart of a method for adjusting a receiver timingof a wireless device in a Coordinated MultiPoint (CoMP) system inaccordance with an example;

FIG. 9 depicts a flow chart of a method for synchronizing a timing of adownlink (DL) transmission of a first cooperating node relative to adownlink transmission of a second cooperating node in a CoordinatedMultiPoint (CoMP) system in accordance with an example;

FIG. 10 illustrates a block diagram of a wireless device and a pluralityof cooperating nodes in accordance with an example; and

FIG. 11 illustrates a diagram of a wireless device in accordance with anexample.

Reference will now be made to the exemplary embodiments illustrated, andspecific language will be used herein to describe the same. It willnevertheless be understood that no limitation of the scope of theinvention is thereby intended.

DETAILED DESCRIPTION

Before the present invention is disclosed and described, it is to beunderstood that this invention is not limited to the particularstructures, process steps, or materials disclosed herein, but isextended to equivalents thereof as would be recognized by thoseordinarily skilled in the relevant arts. It should also be understoodthat terminology employed herein is used for the purpose of describingparticular examples only and is not intended to be limiting. The samereference numerals in different drawings represent the same element.Numbers provided in flow charts and processes are provided for clarityin illustrating steps and operations and do not necessarily indicate aparticular order or sequence.

EXAMPLE EMBODIMENTS

An initial overview of technology embodiments is provided below and thenspecific technology embodiments are described in further detail later.This initial summary is intended to aid readers in understanding thetechnology more quickly but is not intended to identify key features oressential features of the technology nor is it intended to limit thescope of the claimed subject matter.

A Coordinated MultiPoint (CoMP) system may be used to reduceinterference from neighboring nodes in both homogeneous networks andHetNets. In the Coordinated MultiPoint (CoMP) system, the nodes,referred to as cooperating nodes, can also be grouped together withother nodes where the nodes from multiple cells can transmit signals tothe wireless device and receive signals from the wireless device. Thecooperating nodes can be nodes in the homogeneous network or macro nodesand/or lower power nodes (LPN) in the HetNet. Downlink CoMP transmissioncan be divided into two categories: coordinated scheduling orcoordinated beamforming (CS/CB or CS/CBF), and joint processing or jointtransmission (JP/JT). With CS/CB, a given subframe can be transmittedfrom one cell to a given wireless device (UE), and the scheduling,including coordinated beamforming, is dynamically coordinated betweenthe cells in order to control and/or reduce the interference betweendifferent transmissions. For joint processing, joint transmission can beperformed by multiple cells to a wireless device (UE), in which multiplenodes transmit at the same time using the same time and frequency radioresources and/or dynamic cell selection.

In non CoMP systems timing synchronization at the wireless device (e.g.,the UE) can be carried out by using primary synchronization signals(PSS) and/or cell specific reference signals (CRS). In downlink (DL)CoMP systems and deployments with distributed antennas at differentgeographical locations, timing estimation using PSS and/or CRS may notbe accurate since the PSS and/or CRS transmission point (e.g., a macronode 210 in a macro cell 212) may not be the same as a physical downlinkshared channel (PDSCH) transmission point (e.g., a lower power node[LPN] 220 in a LPN cell 222), as illustrated in FIG. 1. In a dynamicpoint selection (DPS) DL CoMP example using a common cell identifier(ID) shown in FIG. 1, a DL transmission 250 (including a PSS and/or aCRS) from the macro node to the wireless device (e.g., a UE 230) and aseparate DL transmission 260 (including data or a PDSCH) from the LPN tothe wireless device can be transmitted at a substantially same time. TheDL transmissions can arrive at the wireless device at different timesdue to different geographical locations of the nodes (e.g., the macronode and the LPN) and/or other factors. The wireless device can besynchronized to the PSS and/or CRS transmission point (e.g., the macronode). For example, an orthogonal frequency-division multiplexing (OFDM)symbol in a macro node transmission 252 and a substantially same OFDMsymbol in a LPN transmission 262 can be received by the wireless device(e.g., UE) at different times due to propagation delays. The OFDM symbolcan include a cyclic prefix (CP). A UE reception of the macro node DLtransmission 254 can have a larger propagation delay 256 than apropagation delay 266 of a UE reception of the LPN DL transmission 264due to the UE being closer to the LPN than the macro node. If the PSSand/or CRS from the macro node are used for timing synchronization, thetiming of the fast Fourier transform (FFT) window 280 used to sample theOFDMA symbol can be synchronized to the macro node DL transmission,which transmission may not be the earnest transmission within thecoordination set. Consequently, transmissions from other nodes (in thecoordination set) with timings of OFDM symbols being in advance withrespect to the FFT sampling window may be applied by a wireless device.Moreover, in some cases the transmission form the macro node may nothave the strongest signal power (e.g., a reference signal received power(RSRP)) and/or provide the data transmission (e.g., the PDSCH). In thesecases, inter-carrier interference (ICI) and inter-symbol interference(ISI) 270 may arise due to incorrect setting of FFT timing at thewireless device. To reduce the ICI and ISI and improve OFDMA symbolreception, the receiver timing can be adjusted, which can shift the FFTwindow. A number of FFT samples of the OFDM symbol can be captured inthe FFT window used to receive the OFDM symbol. Although, a macro nodeand a LPN are illustrated in FIGS. 1-2, any types of nodes in a DL CoMPsystem may be used.

The timing synchronization of a receiver timing of a wireless device maybe modified to use timing estimations generated from node specificreference signals of a CoMP measurement set, where basic timingsynchronization uses the PSS and/or the CRS. A node specific referencesignal can include a channel-state information reference signal(CSI-RS). The receiver timing can be the receiver internal processingtiming, such as the timing where the receiver looks for OFDM symbolsboundaries or the moments where the receiver takes FFTs (e.g., samplesthe OFDM symbols). Because different CSI-RS configurations can beassigned to different geographically separated transmission points(e.g., the macro node and the LPN), the timing estimation can be carriedout for each transmission point independently. The wireless device cancalculate the actual timing for data or a PDSCH reception from multiplenodes based on the multiple timing estimations from CSI-RS.

In an example, the wireless device can receive a plurality of nodespecific reference signals (RSs), such as CSI-RSs, from a plurality ofcooperating nodes (e.g., the macro node and the LPN) in a coordinationset of the CoMP system (e.g., a CoMP measurement set). The coordinationset can include at least two cooperating nodes. A cooperating node caninclude a serving node, a macro node, or a LPN. The wireless device canreceive node specific RSs from at least two cooperating nodes. Thewireless device can generate or calculate a received RS timing from thenode specific RSs for a cooperating node. The wireless device canestimate a composite received RS timing from a plurality of received RStimings. The received RS timings can represent timings from at least twocooperating nodes. The wireless device can adjust the receiver timingbased on the composite received RS timing. The adjusted receiver timingcan be a time a receiver of the wireless device samples, takes, orprocesses the FFT for a received signal or OFDM symbol.

In one embodiment, the wireless device can determine an earliestreceived RS timing from the plurality of received RS timing representingthe various cooperating nodes. The estimated composite received RStiming used to adjust the receiver timing and/or the FFT window can useor include the earliest received RS timing 282. The earliest received RStiming can represent a DL transmission with a shortest propagation delayrelative to other cooperating nodes. The estimated composite received RStiming or a actual PDSCH timing τ_(PDSCH) can be set to the earliesttiming among all calculated timings τ_(CSI-RS) ^((i)) of CoMPmeasurement set, represented by

${\tau_{PDSCH} = {\min\limits_{i}\left( \tau_{{CSI}\text{-}{RS}}^{(i)} \right)}},$

where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is a calculated channel-state information referencesignal (CSI-RS) timing for each node of a CoMP measurement set, min( )is a minimum function, and i is a positive integer representing thenodes in the CoMP measurement set (i.e. there are i nodes in the CoMPmeasurement set). At a wireless device, adjusting the receiver timing orthe FFT window based on the earnest received RS timing can reduce thetimings of signals being advanced with respect to the FFT samplinginterval of the wireless device. In an example, the estimated compositereceived RS timing using the earliest received RS timing can be used injoint transmission (JP/JT) of joint processing (JP), so the FFT samplinginterval can be adjusted correspond to the CSI-RS timing of the nearestthe node. In joint transmission (JT), the PDSCH can be transmitted fromthe plurality of cooperating nodes of coordinated cells.

In another embodiment, the wireless device can determine a minimalreceived RS timing and a maximal received RS timing from the pluralityof received RS timing representing the various cooperating nodes. Theestimated composite received RS timing can be a value or a receiver RStiming substantially between a minimal received RS timing and a maximalreceived RS timing. As shown in FIG. 3, the minimal received RS timing362 can include the earliest received RS timing representing a DLtransmission with a shortest propagation delay relative to othercooperating nodes. The maximal received RS timing 364 can include thelatest received RS timing representing a DL transmission with a longestpropagation delay relative to other cooperating nodes.

In another embodiment, the composite received RS timing used to adjustthe receiver timing and/or the FFT window can be determined orcalculated by a combination of a reference signal received power (RSRP)for the cooperating nodes and the received RS timing generated from thenode specific RSs of the cooperating nodes. For example, the estimatedcomposite received RS timing 284 or an actual timing can be calculatedusing the weighted sum of CSI-RS timings represented by

${\tau_{PDSCH} = \frac{\sum\limits_{i}{{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}\tau_{{CSI}\text{-}{RS}}^{(i)}}}{\sum\limits_{i}{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}}},$

where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(SCI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set,RSRP_(CSI-RS) ^((i)) is CSI-RS antenna port received signal power, i isa positive integer representing the nodes in the CoMP measurement set,and to is a monotonic function of its argument (i.e., functionarguments). Adjusting the receiver timing or the FFT window based on theRSRP can give weight or priority to the received OFDM symbols from thechannels or signals with greatest or strongest signal power. Thecomposite received RS timing using the combination of a reference signalreceived power (RSRP) and the received RS timing for the cooperatingnodes can be using in dynamic point selection (DPS) or dynamic cellselection (DCS) of joint processing (JP). In dynamic cell selection(DCS), PDSCH is transmitted from a single cooperating node in thecoordination set, which can be dynamically selected.

In another embodiment, a sending cooperating node or a controller in acore network can select a selected cooperating node from a plurality ofcooperating nodes to be used for a reference cooperating node inadjusting the receiver timing of the wireless device. The sendingcooperating node can be a same cooperating node or a differentcooperating node from the selected cooperating node. The sendingcooperating node can transmit a selection of the selected cooperatingnode to the wireless device. The wireless device can receive from thecooperating node the selection of the selected cooperating node. Theselection of the selected cooperating node can be transmitted orsignaled in downlink control information (DCI) targeted for the wirelessdevice. The wireless device can receive a plurality of node specific RSfrom the various cooperating nodes. The wireless device can generate asynchronization RS timing from a node specific RS from the selectedcooperating node. The synchronization RS timing can be used to adjustthe receiver timing of the wireless device (for timing synchronization)for received data or a received physical downlink shared channel(PDSCH). The composite received RS timing can include thesynchronization RS timing. In this way, a cooperating node (e.g., thesending cooperating node) or a controller in a core network can selectthe RS timing to be used for the composite received RS timing used toadjust the receiver timing to receive the PDSCH.

FIG. 3 illustrates adjusting a receiver timing of a wireless device in aCoordinated MultiPoint (CoMP) system with two cooperating nodes 310A-B(e.g., a first and second cooperating node) transmitting node specificreference signals (NS-RS) 350A-B to a wireless device 330 in acoordination set 320. The wireless device can be initially synchronizedto the PSS and/or CRS transmission point (e.g., the second cooperatingnode). For example, an OFDM symbol in a first cooperating nodetransmission 352B and a substantially same OFDM symbol in a secondcooperating transmission 352A can be received by the wireless device atdifferent times due to propagation delays. A wireless device (WD)reception of a second cooperating node (ON) DL transmission 354A canhave a larger propagation delay 356A than a propagation 356B delay of awireless device (WD) reception of a first cooperating node (ON) DLtransmission 354B due to the wireless device being closer to the firstcooperating node than the second cooperating node. If the PSS and/or CRSfrom the macro node are used for timing synchronization, the timing ofthe fast Fourier transform (FFT) window 380 used to sample the OFDMsymbol can be synchronized to the macro node DL transmission. Theestimated composite received RS timing 384 used to adjust the receivertiming and/or the FFT window can use or include the earliest received RStiming or can be determined or calculated by a combination of areference signal received power (RSRP) for the cooperating nodes and thereceived RS timing. The cooperating nodes can transmit a node specificRS to the wireless device prior to the wireless device generating thereceived RS timings from the plurality of cooperating nodes.

FIG. 4 illustrates another example of synchronizing a timing of a DLtransmission of a first cooperating node relative to a downlinktransmission of a second cooperating node in a Coordinated Multipoint(CoMP) system to reduce ICI and ISI. The OFDM symbol can be receivedfrom two cooperating nodes a substantially same time. The adjustmenttiming 396 can be made at the transmitter timer of a cooperating node,which can shift an inverse fast Fourier transform (IFFT) modulatingwindow. The IFFT modulator or IFFT module can be used to generatemodulated signals. A wireless device can transmit to the firstcooperating node a timing feedback including the composite received RStiming or the first cooperating node received RS timing generated fromthe node specific RSs from the first cooperating node. The firstcooperating node can receive the timing feedback from the wirelessdevice. The first cooperating node can modify a downlink transmissiontiming (e.g., the first cooperating node DL transmission 392) by anadjustment timing 396 using the composite received RS timing or thefirst cooperating node received RS timing. Modifying the downlinktransmission timing can include shifting (e.g., delaying or advancing)an inverse fast Fourier transform (IFFT) timing of a downlink signalused for the downlink transmission by the composite received RS timingor the first cooperating node received RS timing. The change in thewireless device (WD) reception of the first cooperating node (CN) DLtransmission 394 can reduce the time between a minimal received RStiming and a maximal received RS timing, which can align the receivedOFDM symbols and reduce ICI and ISI. In another example, the downlinktransmission from at least two cooperating nodes in the plurality ofcooperating nodes may be received by the wireless device at asubstantially same time. In another example, the DL transmission of thecooperating nodes may be adjusted to synchronize the reception of the DLtransmission at the wireless device to a specified timing, such as theexisting PSS and/or CRS.

In another example, the receiver timing of the wireless device can beadjusted using the information from the node specific RS from aplurality of cooperating nodes and the transmitter timing of at leastone cooperating node can be adjusted using the timing feedback to reducethe time between a minimal received RS timing and a maximal received RStiming.

In one example, the OFDM symbols and node specific RSs can representelements of a radio frame structure transmitted on the physical (PHY)layer in a downlink transmission or uplink transmission between a node(or eNodeB) and the wireless device (or UE) using a generic long termevolution (LTE) frame structure, as illustrated in FIG. 5. While an LTEframe structure is illustrated, a frame structure for an IEEE 802,16standard (WiMax), an IEEE 802.11 standard (WiFi), or another type ofcommunication standard using OFDM may also be used.

FIG. 5 illustrates a downlink radio frame structure type 2. In theexample, a radio frame 100 of a signal used to transmit the data can beconfigured to have a duration, T_(f), of 10 milliseconds (ms). Eachradio frame can be segmented or divided into ten subframes 110 i thatare each 1 ms long. Each subframe can be further subdivided into twoslots 120 a and 120 b, each with a duration, T_(slot), of 0.5 ms. Eachslot for a component carrier (CC) used by the transmitting station andthe receiving station can include multiple resource blocks (RBs) 130 a,130 b, 130 i, 130 m, and 130 n based on the CC frequency bandwidth. TheCC can have a carrier frequency having a bandwidth and center frequency.Each RB (physical RB or PRB) 130 i can include 12-15 kHz subcarriers 136(on the frequency axis) and 6 or 7 orthogonal frequency-divisionmultiplexing (OFDM) symbols 132 (on the time axis) per subcarrier. TheRB can use seven OFDM symbols if a short or normal cyclic prefix isemployed. The RB can use six OFDM symbols if an extended cyclic prefixis used. The resource block can be mapped to 84 resource elements (REs)140 i using short or normal cyclic prefixing, or the resource block canbe mapped to 72 REs (not shown) using extended cyclic prefixing. The REcan be a unit of one OFDM symbol 142 by one subcarrier (i.e., 15 kHz)146. Each RE can transmit two bits 150 a and 150 b of information in thecase of quadrature phase-shift keying (QPSK) modulation. Other types ofmodulation may be used, such as 16 quadrature amplitude modulation (QAM)or 64 QAM to transmit a greater number of bits in each RE, or bi-phaseshift keying (BPSK) modulation to transmit a lesser number of bits (asingle bit) in each RE. The RB can be configured for a downlinktransmission from the eNodeB to the UE, or the RB can be configured foran uplink transmission from the UE to the eNodeB.

Reference signals can be transmitted by OFDM symbols via resourceelements in the resource blocks. Reference signals (or pilot signals ortones) can be a known signal used for various reasons, such as tosynchronize timing, estimate a channel, and/or noise in the channel.Reference signals can be received and transmitted by transmittingstations and mobile communication devices. Different types of referencesignals (RS) can be used in a RB. For example, in LTE systems, downlinkreference signal types can include a cell-specific reference signal(CRS), a multicast\broadcast single-frequency network (MBSFN) referencesignal, a UE-specific reference signal (UE-specific RS or UE-RS) or ademodulation reference signal (DMRS), positioning reference signal(PRS), and a channel-state information reference signal (CSI-RS).

The CRS can be transmitted in downlink subframes in a cell supporting aPDSCH. Data is transmitted from an eNodeB to a UE via a PDSCH. The MBSFNreference signal can be transmitted when the physical multicast channel(PMCH) is transmitted in a MBSFN subframe. The UE-RS or DMRS can betransmitted in downlink subframes supporting the PDSCH. The UE-RS (DMRS)can be transmitted within the resource blocks assigned for downlinkshared channel (DL-SCH) transmission to a specific terminal (e.g.,mobile communication device), used for beamforming to a single UE usingmultiple antennas, and used for PDSCH demodulation. The PRS can betransmitted in an RB in downlink subframe configured for PRStransmission, but may not be mapped to a physical broadcast channel(PBCH), a primary synchronization signal (PSS), or a secondarysynchronization signal (SSS). The CSI-RS can be used for downlinkchannel quality measurements.

FIG. 6 illustrates an example flow chart of timing synchronization 560and additional timing synchronization 580 for a downlink (DL)transmission in a Coordinated MultiPoint (CoMP) system. Initially,timing estimation for a receiver for a wireless device can be generatedusing PSS and/or CRS 562 from a cooperating node. A CoMP measurement setconfiguration 572 can be generated by at least one cooperating node. Inanother embodiment, the CoMP measurement set configuration 572 may bereceived by at least one cooperating node from a controller in a corenetwork. At least a segment of the CoMP measurement set configurationcan be sent to the wireless device. The segment of the CoMP measurementset transmitted to the wireless device can include the cooperating nodesin coordination set used for the measurement of the node specific RSs(e.g., CSI-RSs). The additional timing synchronization can include atiming estimation for each CSI-RS antenna port in CoMP measurement set582 and a calculation of a composite received RS timing from theestimated set of timings 584 used to adjust or generate the actualtiming of the receiver of the wireless device.

The additional timing synchronization using the node specific RS orCSI-RS over controlling timing synchronization with just the PSS, SSS,and/or CRS signals can allow the receiver timing to be adjusted toreceive the data OFDM symbols from different cooperating nodes so that amajority of the OFDM symbol boundaries fall within a guard interval ofOFDM symbol, which can reduce the ICI and ISI. The receiver timing caninclude the receiver internal processing timing, the timing where thereceiver looks for OFDM symbols boundaries, or the moments where thereceiver takes or samples the FFTs. The additional timingsynchronization uses several received reference signal timings fromdifferent cooperating nodes instead of just the PSS, SSS, and/or CRSsignals from a single node. Each received reference signal (RS) timingcan be from an ith cooperating node, where i is a positive integerrepresenting the nodes in the CoMP measurement set. The OFDM symbolsboundaries can be in the signal received from ith cooperating node,which can include the serving node. The values for the received RStimings can be measured or generated using the node specific RSs orCSI-RSs from the ith cooperating node. The timings can include possibledelays such as transmitter (TX) delay, propagation delay, receiver (RX)delay, and other processing delay.

FIG. 7 illustrates a OFDM demodulator including a FFT demodulator in areceiver (RX) used for a downlink in a wireless device and an OFDMmodulator including an IFFT modulator in a transmitter used for adownlink in a cooperating node. The timing of the FFT demodulator may beadjusted for the OFDM symbols using the additional timingsynchronization.

A wireless communication system can be subdivided into various sectionsreferred to as layers. In the LTE system, communication layers caninclude the physical (PHY), media access control (MAC), radio linkcontrol (RLC), packet data convergence protocol (PDCP), and radioresource control (RRC) layers. The physical layer can include the basichardware transmission components of a wireless communication system 400,as illustrated in FIG. 7. A basic multiple-input multiple-output (MIMO)system is used for simplicity in illustrating the basic hardwaretransmission components, but the components can also be adapted for acomplex MIMO system, a SISO system, or similar system. For example in aMIMO system, at the transmitter 410, binary input data 420 can beprotected through encoding using a channel encoder 422, interleavedagainst fading phenomenon using an interleaver 424, and mapped toimprove reliability using a mapper 426. The mapped data can be separatedinto layers for antenna ports by a transmitter (TX) beamformer 434 andthe layers can be OFDM modulated into OFDM symbols using modulators428A-B. The modulators can use an inverse fast Fourier transform (IFFT)algorithm to compute the inverse discrete Fourier transform (IDFT) togenerate modulated signals (vector x for each antenna port). Themodulated signals can be converted to analog signals withdigital-to-analog converters (DACs) 430A-B. The analog signals can betransmitted via radio frequency (RF) transmitters (Txs) 432A-Bconfigured to send the signal to transmitter antennas 440A-B operable tocommunicate the signal. The analog signals will follow a path referredto as a channel 450. The physical layer can include other components(not shown), such as series-to-parallel (S/P) converters,parallel-to-serial (P/S) converters, cyclic prefix (CP) inserters anddeleters, guardband inserters and deleters, and other desiredcomponents.

The signal transmitted through a channel 450 can be subject to noise 452and interference 454. The noise and interference is represented as anaddition 456 to the channel signal, which can be received by receiverantennas 490A-B and one or more radio frequency (RF) receivers (Rxs)482A-B at the receiver 460. The channel signal combined with the noiseand interference can be converted to a digital modulated signal withanalog-to-digital converters (ADCs) 480A-B, The digital signal can beOFDM demodulated using demodulators 478A-B. The demodulators can use afast Fourier transform (FFT) algorithm to compute the discrete Fouriertransform (DFT) to generate demodulated signals (vector y for eachantenna port). A channel estimator 462 can use the demodulated signal toestimate the channel 450 and the noise and interference that occurs inthe channel. The channel estimator can include a feedback generator orbe in communication with the feedback generator, which can generate aphysical uplink shared channel (PUSCH) feedback report, such as achannel quality indicator (CQI) report, a precoding matrix indicator(PMI) report, or a transmission rank indicator (RI) report. The CQI canbe used to assist the MIMO transmissions modes. The demodulated signalscan be combined using a MIMO decoder 484, demapped using a demapper 476,deinterleaved using a deinterleaver 474, and decoded by a channeldecoder 472 to generate binary output data 470 that can be used by otherlayers of the receiving station.

Another example provides a method 500 for adjusting a receiver timing ofa wireless device in a Coordinated MultiPoint (CoMP) system, as shown inthe flow chart in FIG. 8. The method may be executed as instructions ona machine, where the instructions are included on at least one computerreadable medium or one non-transitory machine readable storage medium.The method includes the operation of receiving a plurality of nodespecific reference signals (RSs) at a wireless device from a pluralityof cooperating nodes in a coordination set of the CoMP system, whereinthe coordination set includes at least two cooperating nodes, as inblock 510. The operation of estimating a composite received RS timingfrom a plurality of received RS timings generated from the plurality ofnode specific RSs, wherein the received RS timings represent timingsfrom the at least two cooperating nodes follows, as in block 520. Thenext operation of the method can be adjusting the receiver timing basedat least in part on the composite received RS timing, as in block 530.

The node specific RS can include a channel-state information referencesignal (CSI-RS). The adjusted receiver timing can be a time a receiverof the wireless device processes the fast Fourier transform (FFT) for areceived signal.

In an embodiment, the operation of estimating a composite received RStiming can further include selecting an earliest received RS timing forthe composite received RS timing. The composite received RS timing canbe represented by

${\tau_{PDSCH} = {\min\limits_{i}\left( \tau_{{CSI}\text{-}{RS}}^{(i)} \right)}},$

where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set, min( ) is aminimum function, and i is a positive integer representing the nodes inthe CoMP measurement set.

In another embodiment, the operation of estimating a composite receivedRS timing can further include selecting a receiver RS timingsubstantially between a minimal received RS timing and a maximalreceived RS timing. The minimal received RS timing can include thetiming generated from the first received node specific RS of a firstcooperating node and the maximal received RS timing can include thetiming generated from the last received node specific RS of a lastcooperating node. In an example, the composite received RS timing can bedetermined by a combination of a reference signal received power (RSRP)for the cooperating nodes and the received RS timing generated from thenode specific RSs of the cooperating nodes. In another example, thecomposite received RS timing can be represented by

${\tau_{PDSCH} = \frac{\sum\limits_{i}{{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}\tau_{{CSI}\text{-}{RS}}^{(i)}}}{\sum\limits_{i}{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}}},$

where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set,RSRP_(CSI-RS) ^((i)) is CSI-RS antenna port reference signal receivedpower (RSRP), i is a positive integer representing the nodes in the CoMPmeasurement set, and f( ) is a monotonic function of its argument.

The method can further include the wireless device transmitting from toa cooperating node a timing feedback including the composite received RStiming. In another example, the method can further include the wirelessdevice transmitting from to a cooperating node a timing feedbackincluding a received RS timing generated from the node specific RSs fromthe cooperating node. The node specific RS can include a primarysynchronization signal (PSS), a secondary synchronization signal (SSS),a cell specific reference signal (CRS), or a channel-state informationreference signal (CSI-RS).

Another example provides a method 600 for synchronizing a timing of adownlink (DL) transmission of a first cooperating node relative to adownlink transmission of a second cooperating node in a CoordinatedMultiPoint (CoMP) system, as shown in the flow chart in FIG. 9. Themethod may be executed as instructions on a machine, where theinstructions are included on at least one computer readable medium orone non-transitory machine readable storage medium. The method includesthe operation of receiving at the first cooperating node from a wirelessdevice a timing feedback, wherein timing feedback includes at least onereceived reference signal (RS) timing generated from a node specific RSof at least one cooperating node, as in block 610. The operation ofmodifying a downlink transmission timing at the first cooperating nodeby an adjustment timing using the timing feedback follows, as in block620.

The timing feedback includes a composite received RS timing or the firstcooperating node received RS timing. The composite received RS timingcan be estimated from a plurality of received RS timings representingtimings from at least two cooperating nodes. The first cooperating nodereceived RS timing can be generated from the node specific RSs from thefirst cooperating node. The received RS timings can be generated fromthe plurality of node specific RSs.

In an example, the composite received RS timing can include a firstcooperating node received RS timing generated from the node specific RSsfrom the first cooperating node. The node specific reference signalincludes a channel-state information reference signal (CSI-RS). Thedownlink transmission includes data or a physical downlink sharedchannel (PDSCH). The operation of modifying the downlink transmissiontiming can further include shifting an inverse fast Fourier transform(IFFT) timing of a downlink signal used for the downlink transmissionbased on the composite received RS timing or the first cooperating nodereceived RS timing. The method can further include the first cooperatingnode (e.g., the sending cooperating node) selecting a selectedcooperating node from a plurality of cooperating nodes. A node specificRS from the selected cooperating node can be used by the wireless deviceto generate a synchronization RS timing, and the synchronization RStiming can be used for timing synchronization for received data or areceived physical downlink shared channel (PDSCH). the first cooperatingnode can transmit a selection of the selected cooperating node to thewireless device. The synchronization RS timing can be used to adjust areceiver timing of the wireless device for received data or the receivedPDSCH. The method can further include the first cooperating nodetransmitting a node specific RS to the wireless device prior toreceiving the timing feedback.

FIG. 10 illustrates example cooperating nodes 710A-B and an examplewireless device 720 in a Coordinated MultiPoint (CoMP) system. Thecooperating nodes can include a macro node (e.g., macro-eNB) or a lowpower node (e.g., micro-eNB, a pico-eNB, a femto-eNB, or a HeNB).

The wireless device 720 (e.g., UE) can be in communication with thecooperating nodes 710A-B. The wireless device can include a timingestimation device 718 for estimating a receiver timing of a wirelessdevice in a Coordinated MultiPoint (CoMP) system. The timing estimationdevice can include downlink receiving module 722 and a timing estimator724. In some embodiments, the timing estimation device can include atiming adjustment module 726 and uplink (UL) transmitting module 728.The wireless device can include a transceiver configured to receive DLtransmission information from the cooperating nodes and transmit ULtransmission information to the cooperating nodes.

The downlink receiving module 722 can be configured to receive aplurality of node specific reference signals (RSs) at a wireless devicefrom a plurality of cooperating nodes in a coordination set of the CoMPsystem. The coordination set can include at least two cooperating nodes.The downlink receiving module can be further configured to receive aselection of a selected cooperating node. The selected cooperating nodecan be selected by or a controller in a core network or a cooperatingnode from a plurality of cooperating nodes. A node specific RS from theselected cooperating node can be used by the wireless device to generatea synchronization RS timing, and the synchronization RS timing can beused for timing synchronization or to adjust a receiver timing of thewireless device for received data or a received physical downlink sharedchannel (PDSCH). The timing estimator 724 can be configured to estimatea composite received RS timing from a plurality of received RS timingsgenerated from the plurality of node specific RSs. The received RStimings can represent timings from the at least two cooperating nodes.The node specific RS includes a channel-state information referencesignal (CSI-RS). In an example, the timing estimator can be configuredto select an earliest received RS timing for the composite received RStiming. The composite received RS timing can be represented by

${\tau_{PDSCH} = {\min\limits_{i}\left( \tau_{{CSI}\text{-}{RS}}^{(i)} \right)}},$

where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set, min( ) is aminimum function, and i is a positive integer representing the nodes inthe CoMP measurement set. In another example, the timing estimator canbe configured to select a receiver RS timing substantially between aminimal received RS timing and a maximal received RS timing using thecomposite received RS timing. In another example, the timing estimatorcan be configured determine the composite received RS timing from acombination of a reference signal received power (RSRP) for thecooperating nodes and the received RS timing generated from the nodespecific RSs of the cooperating nodes. The composite received RS timingis represented by

${\tau_{PDSCH} = \frac{\sum\limits_{i}{{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}\tau_{{CSI}\text{-}{RS}}^{(i)}}}{\sum\limits_{i}\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}},$

where τ_(PDSCH) is a physical downlink shared channel(PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set,RSRP_(CSI-RS) ^((i)) is CSI-RS antenna port reference signal receivedpower (RSRP), i is a positive integer representing the nodes in the CoMPmeasurement set, and f( ) is a monotonic function of its argument.

The timing adjustment module 726 can be configured to adjust thereceiver timing based on the composite received RS timing. The adjustedreceiver timing can be a time a receiver of the wireless deviceprocesses the fast Fourier transform (FFT) for a received signal. Thetime can represent a boundary of a FFT window. The uplink transmittingmodule 728 can be configured to transmit to a cooperating node a timingfeedback including the composite received RS timing or a received RStiming generated from the node specific RSs from the cooperating node.The wireless device can include a user equipment (UE) and a mobilestation (MS). The wireless device can configured to connect to at leastone of a wireless local area network (WLAN), a wireless personal areanetwork (WPAN), and a wireless wide area network (WWAN). The wirelessdevice can include an antenna, a touch sensitive display screen, aspeaker, a microphone, a graphics processor, an application processor,internal memory, or a non-volatile memory port.

Each cooperating node 710A-B can include a timing synchronization device708A-B for synchronizing a timing of a downlink (DL) transmission of afirst cooperating node relative to a downlink transmission of a secondcooperating node in a Coordinated MultiPoint (CoMP) system. The timingsynchronization device can include a downlink transmitting module712A-B, an uplink receiving module 714A-B, and a timing modificationmodule 716A-B. In an example, the timing synchronization device caninclude a selection module (not shown). In another example, theselection module can be included in a controller in a core network. Thecooperating nodes can be in coordination set 740 of the CoMP system andcommunicate with each other via a backhaul link 750. The backhaul linkcan include X2 signaling or backhaul link signaling via a wiredconnection, a wireless connection, or an optical fiber connection. Thecommunication between cooperating nodes can include COMP measurement setinformation.

The uplink receiving module 714A-B can be configured to receive from awireless device a timing feedback. The timing feedback can include atleast one received reference signal (RS) timing generated from a nodespecific RS of at least one cooperating node. The timing feedback caninclude a composite received reference signal (RS) timing or a firstcooperating node received RS timing. The composite received RS timingcan be estimated from a plurality of received RS timings representingtimings from at least two cooperating nodes and the received RS timingscan be generated from the plurality of node specific RSs. The firstcooperating node received RS timing can be generated from the nodespecific RSs from the first cooperating node. The timing modificationmodule 716A-B can be configured to modify a downlink transmission timingat the first cooperating node by an adjustment timing using the timingfeedback. The node specific reference signal includes a channel-stateinformation reference signal (CSI-RS). The timing modification modulecan be further configured to shift a fast inverse Fourier transform(IFFT) timing of a downlink signal used for the downlink transmission bythe composite received RS timing or a cooperating node received RStiming. A downlink transmitting module 712A-B can be configured totransmit a node specific RS to the wireless device. The selection modulecan be configured to select a selected cooperating node from a pluralityof cooperating nodes. A node specific RS from the selected cooperatingnode can be used by the wireless device to generate a synchronization RStiming, and the synchronization RS timing can be used for timingsynchronization for received data or a received physical downlink sharedchannel (PDSCH). The downlink transmitting module can be furtherconfigured to transmit a selection of the selected cooperating node tothe wireless device. The synchronization RS timing can be used to adjusta receiver timing of the wireless device for received data or thereceived PDSCH. The cooperating node can include a macro node, a lowpower node (LPN), a macro evolved Node B (macro-eNB), a micro-eNB, apica-eNB, a femto-eNB, or a home eNB (HeNB).

FIG. 11 provides an example illustration of the wireless device, such asa user equipment (UE), a mobile station (MS), a mobile wireless device,a mobile communication device, a tablet, a handset, or other type ofmobile wireless device. The wireless device can include one or moreantennas configured to communicate with a node, such as a macro node, alow power node (LPN), or, transmission station, such as a base station(BS), an evolved Node B (eNB), a base band unit (BBU), a remote radiohead (RRH), a remote radio equipment (RRE), a relay station (RS), aradio equipment (RE), or other type of wireless wide area network (WWAN)access point. The wireless device can be configured to communicate usingat least one wireless communication standard including 3GPP LTE, WiMAX,High Speed Packet Access (HSPA), Bluetooth, and WiFi. The wirelessdevice can communicate using separate antennas for each wirelesscommunication standard or shared antennas for multiple wirelesscommunication standards. The wireless device can communicate in awireless local area network (WLAN), a wireless personal area network(WPAN), and/or a WWAN.

FIG. 11 also provides an illustration of a microphone and one or morespeakers that can be used for audio input and output from the wirelessdevice. The display screen may be a liquid crystal display (LCD) screen,or other type of display screen such as an organic light emitting diode(OLED) display. The display screen can be configured as a touch screen.The touch screen may use capacitive, resistive, or another type of touchscreen technology. An application processor and a graphics processor canbe coupled to internal memory to provide processing and displaycapabilities. A non-volatile memory port can also be used to providedata input/output options to a user. The non-volatile memory port mayalso be used to expand the memory capabilities of the wireless device. Akeyboard may be integrated with the wireless device or wirelesslyconnected to the wireless device to provide additional user input. Avirtual keyboard may also be provided using the touch screen.

Various techniques, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, non-transitory computerreadable storage medium, or any other machine-readable storage mediumwherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing thevarious techniques. In the case of program code execution onprogrammable computers, the computing device may include a processor, astorage medium readable by the processor (including volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. The volatile and non-volatile memoryand/or storage elements may be a RAM, EPROM, flash drive, optical drive,magnetic hard drive, or other medium for storing electronic data. Thebase station and wireless device may also include a transceiver module,a counter module, a processing module, and/or a clock module or timermodule. One or more programs that may implement or utilize the varioustechniques described herein may use an application programming interface(API), reusable controls, and the like. Such programs may be implementedin a high level procedural or object oriented programming language tocommunicate with a computer system. However, the program(s) may beimplemented in assembly or machine language, if desired. In any case,the language may be a compiled or interpreted language, and combinedwith hardware implementations.

It should be understood that many of the functional units described inthis specification have been labeled as modules, in order to moreparticularly emphasize their implementation independence. For example, amodule may be implemented as a hardware circuit comprising custom VLSIcircuits or gate arrays, off-the-shelf semiconductors such as logicchips, transistors, or other discrete components. A module may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions, which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.The modules may be passive or active, including agents operable toperform desired functions.

Reference throughout this specification to “an example” means that aparticular feature, structure, or characteristic described in connectionwith the example is included in at least one embodiment of the presentinvention. Thus, appearances of the phrases “in an example” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary. In addition, various embodiments and example of the presentinvention may be referred to herein along with alternatives for thevarious components thereof. It is understood that such embodiments,examples, and alternatives are not to be construed as defactoequivalents of one another, but are to be considered as separate andautonomous representations of the present invention.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of layouts, distances, network examples, etc., to provide athorough understanding of embodiments of the invention. One skilled inthe relevant art will recognize, however, that the invention can bepracticed without one or more of the specific details, or with othermethods, components, layouts, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring aspects of the invention.

While the forgoing examples are illustrative of the principles of thepresent invention in one or more particular applications, it will beapparent to those of ordinary skill in the art that numerousmodifications in form, usage and details of implementation can be madewithout the exercise of inventive facility, and without departing fromthe principles and concepts of the invention. Accordingly, it is notintended that the invention be limited, except as by the claims setforth below,

1-30. (canceled)
 31. A method for adjusting a receiver timing of awireless device in a Coordinated MultiPoint (CoMP) system, comprising:receiving a plurality of node specific reference signals (RSs) at awireless device from a plurality of cooperating nodes in a coordinationset of the CoMP system, wherein the coordination set includes at leasttwo cooperating nodes; and estimating a composite received RS timingfrom a plurality of received RS timings generated from the plurality ofnode specific RSs, wherein the received RS timings represent timingsfrom the at least two cooperating nodes; and adjusting the receivertiming based at least in part on the composite received RS timing. 32.The method of claim 31, wherein the node specific RS includes achannel-state information reference signal (CSI-RS).
 33. The method ofclaim 31, wherein the adjusted receiver timing is a time a receiver ofthe wireless device processes the fast Fourier transform (FFT) for areceived signal.
 34. The method of claim 31, wherein estimating thecomposite received RS timing further comprises selecting an earliestreceived RS timing for the composite received RS timing.
 35. The methodof claim 34, wherein the composite received RS timing is represented by${\tau_{PDSCH} = {\min\limits_{i}\left( \tau_{{CSI}\text{-}{RS}}^{(i)} \right)}},$where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set, min( ) is aminimum function, and i is a positive integer representing the nodes inthe CoMP measurement set.
 36. The method of claim 31, wherein estimatingthe composite received RS timing further comprises selecting a receiverRS timing substantially between a minimal received RS timing and amaximal received RS timing.
 37. The method of claim 36, wherein thecomposite received RS timing is determine by a combination of areference signal received power (RSRP) for the cooperating nodes and thereceived RS timing generated from the node specific RSs of thecooperating nodes.
 38. The method of claim 36, wherein the compositereceived RS timing is represented by${\tau_{PDSCH} = \frac{\sum\limits_{i}{{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}\tau_{{CSI}\text{-}{RS}}^{(i)}}}{\sum\limits_{i}{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}}},$where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set,RSRP_(CSI-RS) ^((i)) is CSI-RS antenna port reference signal receivedpower (RSRP), i is a positive integer representing the nodes in the CoMPmeasurement set, and f( ) is a monotonic function of function arguments.39. The method of claim 31, further comprising: transmitting from thewireless device to a cooperating node a timing feedback including thecomposite received RS timing or a cooperating node received RS timinggenerated from the node specific RSs from the cooperating node.
 40. Themethod of claim 31, wherein the node specific RS is selected from thegroup consisting of a primary synchronization signal (PSS), a secondarysynchronization signal (SSS), a cell specific reference signal (CRS),and a channel-state information reference signal (CSI-RS), andcombinations thereof.
 41. At least one machine readable mediumcomprising a plurality of instructions adapted to be executed toimplement the method of claim
 31. 42. A timing estimation device forestimating a receiver timing of a wireless device in a CoordinatedMultiPoint (CoMP) system, comprising: a downlink receiving moduleconfigured to receive a plurality of node specific reference signals(RSs) at a wireless device from a plurality of cooperating nodes in acoordination set of the CoMP system, wherein the coordination setincludes at least two cooperating nodes; and a timing estimatorconfigured to estimate a composite received RS timing from a pluralityof received RS timings generated from the plurality of node specificRSs, wherein the received RS timings represent timings from the at leasttwo cooperating nodes.
 43. The timing estimation device of claim 42,wherein the node specific RS includes a channel-state informationreference signal (CSI-RS).
 44. The timing estimation device of claim 42,further comprising: a timing adjustment module configured to adjust thereceiver timing based on the composite received RS timing.
 45. Thetiming estimation device of claim 44, wherein the adjusted receivertiming is a time a receiver of the wireless device processes the fastFourier transform (FFT) for a received signal.
 46. The timing estimationdevice of claim 42, wherein the timing estimator is configured to selectan earliest received RS timing for the composite received RS timing. 47.The timing estimation device of claim 46, wherein the composite receivedRS timing is represented by${\tau_{PDSCH} = {\min\limits_{i}\left( \tau_{{CSI}\text{-}{RS}}^{(i)} \right)}},$where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set, min( ) is aminimum function, and i is a positive integer representing the nodes inthe CoMP measurement set.
 48. The timing estimation device of claim 42,wherein the timing estimator is configured to select a receiver RStiming substantially between a minimal received RS timing and a maximalreceived RS timing.
 49. The timing estimation device of claim 48,wherein the composite received RS timing is represented by${\tau_{PDSCH} = \frac{\sum\limits_{i}{{f\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}\tau_{{CSI}\text{-}{RS}}^{(i)}}}{\sum\limits_{i}\left( {RSRP}_{{CSI}\text{-}{RS}}^{(i)} \right)}},$where τ_(PDSCH) is a physical downlink shared channel (PDSCH) timing,τ_(CSI-RS) ^((i)) is each of calculated channel-state informationreference signal (CSI-RS) timings of a CoMP measurement set,RSRP_(CSI-RS) ^((i)) is CSI-RS antenna port reference signal receivedpower (RSRP), i is a positive integer representing the nodes in the CoMPmeasurement set, and f( ) is a monotonic function of function arguments.50. The timing estimation device of claim 42, further comprising: auplink transmitting module configured to transmit to a cooperating nodea timing feedback including the composite received RS timing.
 51. Thetiming estimation device of claim 42, wherein the wireless deviceincludes the timing estimation device and the wireless device isselected from the group consisting of a user equipment (UE) and a mobilestation (MS), wherein the wireless device is configured to connect to atleast one of a wireless local area network (WLAN), a wireless personalarea network (WPAN), and a wireless wide area network (WWAN), whereinthe wireless device includes an antenna, a touch sensitive displayscreen, a speaker, a microphone, a graphics processor, an applicationprocessor, internal memory, a non-volatile memory port, or combinationsthereof.
 52. A method for synchronizing a timing of a downlink (DL)transmission of a first cooperating node relative to a downlinktransmission of a second cooperating node in a Coordinated MultiPoint(CoMP) system, comprising: receiving at the first cooperating node froma wireless device a timing feedback, wherein timing feedback includes atleast one received reference signal (RS) timing generated from a nodespecific RS of at least one cooperating node; and modifying a downlinktransmission timing at the first cooperating node by an adjustmenttiming using the timing feedback.
 53. The method of claim 52, whereinthe timing feedback includes a composite received RS timing or the firstcooperating node received RS timing, wherein the composite received RStiming is estimated from a plurality of received RS timings representingtimings from at least two cooperating nodes or a first cooperating nodereceived RS timing generated from node specific RSs from the firstcooperating node, and the received RS timings are generated from theplurality of node specific RSs.
 54. The method of claim 52, wherein thenode specific reference signal includes a channel-state informationreference signal (CSI-RS), and the downlink transmission includes dataor a physical downlink shared channel (PDSCH).
 55. The method of claim52, wherein modifying a downlink transmission timing further comprises:shifting an inverse fast Fourier transform (IFFT) timing of a downlinksignal used for the downlink transmission by the composite received RStiming or the first cooperating node received RS timing.
 56. The methodof claim 52, further comprising prior to receiving the timing feedback:selecting, at the first cooperating node, a selected cooperating nodefrom a plurality of cooperating nodes, wherein a node specific RS fromthe selected cooperating node is used by the wireless device to generatea synchronization RS timing, and the synchronization RS timing is usedfor timing synchronization for received data or a received physicaldownlink shared channel (PDSCH); transmitting a selection of theselected cooperating node to the wireless device, wherein thesynchronization RS timing is used to adjust a receiver timing of thewireless device for received data or the received PDSCH; andtransmitting a node specific RS from the first cooperating node to thewireless device.
 57. At least one machine readable medium comprising aplurality of instructions adapted to be executed to implement the methodof claim
 52. 58. A timing synchronization device for synchronizing atiming of a downlink (DL) transmission of a first cooperating noderelative to a downlink transmission of a second cooperating node in aCoordinated MultiPoint (CoMP) system, comprising: a uplink receivingmodule configured to receive from a wireless device a timing feedback,wherein timing feedback includes at least one received reference signal(RS) timing generated from a node specific RS of at least onecooperating node; and a timing modification module configured to modifya downlink transmission timing by an adjustment timing using the timingfeedback.
 59. The timing synchronization device of claim 58, wherein thenode specific reference signal includes a channel-state informationreference signal (CSI-RS), and the timing feedback includes a compositereceived reference signal (RS) timing or the first cooperating nodereceived RS timing, wherein the composite received RS timing isestimated from a plurality of received RS timings representing timingsfrom at least two cooperating nodes, the first cooperating node receivedRS timing is generated from the node specific RSs from the firstcooperating node, and the received RS timings are generated from theplurality of node specific RSs.
 60. The timing synchronization device ofclaim 58, further comprising: a downlink transmitting module configuredto transmit a node specific RS to the wireless device, and wherein thetiming modification module is further configured to shift a fast inverseFourier transform (IFFT) timing of a downlink signal used for thedownlink transmission by the adjustment timing using the timingfeedback.